Скачать или смотреть Fix “Cannot Read Properties of Undefined” in JavaScript (ES2020)

Ever seen the dreaded JavaScript error “Cannot read properties of undefined” and watched your app crash?
If you work with APIs or deeply nested objects, this happens more often than you’d like.

In this video, we break down two modern JavaScript features—Optional Chaining (?.) and Nullish Coalescing (??)—that help you write safer, cleaner, and more readable code. Instead of adding endless defensive checks, you’ll learn how to handle missing data gracefully using simple, expressive syntax.

We start by looking at the traditional way developers used to protect against runtime errors using multiple logical checks. While it works, it quickly becomes verbose and hard to maintain as applications grow. From there, we introduce optional chaining and show how it safely stops execution when a value is null or undefined—without crashing your app.

Next, we cover a common mistake developers make when setting default values using the logical OR operator. You’ll see why valid values like 0 or empty strings can cause unexpected bugs, especially in UI and configuration settings. That’s where nullish coalescing comes in, allowing you to apply defaults only when values are truly missing.

Finally, we combine both features to demonstrate a clean, real-world pattern that works perfectly with API responses, frontend state, and cloud-based applications.

Whether you’re building frontend interfaces, working with integrations, or handling data from APIs in modern software development environments, these features will help you avoid bugs and improve code quality.

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3️⃣ Detailed Timeline

00:00 – Title card
00:06 – Common JavaScript runtime error explained
00:20 – Why deep object access fails with APIs
00:38 – Traditional defensive null checks
01:00 – Introducing optional chaining (?.)
01:22 – Safe access example with missing properties
01:44 – Problem with logical OR (||) defaults
02:05 – Nullish coalescing (??) explained
02:25 – Combining ?. and ?? for clean code
02:45 – Real-world benefits and takeaway
02:58 – Outro and call to action